Environmental chemicals, acting alone or in combination, are probably the major cause of cancer in humans. The Program Project is designed to utilize the expertise and facilities at the Wistar Institute to study exogenous and endogenous components of environmental carcinogenesis and to serve as the nucleus of an Environmental Carcinogenesis Center at the Institute. In vitro and in vivo model systems will be used to investigate the mechanisms by which environmental chemicals interact with the host cell and with each other and the mechanisms by which the host can respond to these chemicals. This multidisciplinary approach to a multifaceted problem will increase our understanding of how environmental chemicals cause cancer.